Kondo Effect at Molecule-Metal-Interfaces: Investigation by Angle-resolved Photoemission and Orbital Tomography

在某些情况下，在分子和金属表面之间的界面处观察到近藤效应的发生。通过局域态与传导电子池的相互作用，这种效应可以增加费米能级处的态密度，从而对传输和接触特性产生关键影响。除了对相关模型系统进行广泛的STM和输运研究外，导致分子近藤效应发生的基本关系，特别是所涉及的单粒子态的性质和局部磁性，还没有完全澄清。在这方面，角分辨光电子能谱（ARPES）提供了获取微观信息的途径，这是STM所不能或只能获得的非常有限的信息。采用角信息允许的字符和所涉及的局域态的对称性的声明。在理想情况下，有机吸附物体系的分子单粒子轨道可以重建。通过研究入射光的偏振方向和光子能量对光电发射信号的依赖性，提供了额外的信息。除此之外，相关的模型参数可以从ARPES实验中得到，基于该模型，可以获得Kondo模型或单杂质安德森模型（SIAM）中微观关系的一致图像。本项目将在前期工作的基础上，利用ARPES系统地研究分子-金属界面的近藤效应，并特别回答以下问题：（i）近藤共振等众多粒子信号与哪种对称性有关？我们能从对称性中了解这些状态的本质吗？ 在近藤效应的发生所涉及的国家的性质还不清楚，将来自ARPES的角度信息和可变光偏振的实验。(ii)从近藤共振和芯能级谱的温度依赖性确定特征温度或能量标度。实验确定大温度范围内光发射强度的温度依赖性提供了获得相关特征能量尺度的途径。(iii)在实践中，相关的模型参数是否可以系统地改变？在SIAM的框架中，分子-基底界面系统的描述涉及模型参数，这些参数可以通过光谱或通过与相应的计算进行比较来确定。这些参数的外部控件允许操作接口属性。

In certain cases the occurrence of a Kondo effect is observed at interfaces between molecules and metallic surfaces. By the interaction of a localized state with the bath of conduction electrons this effect can increase the density of states at the Fermi level and thus crucially influence the transport and contact properties. Besides extensive STM and transport investigations on relevant model systems the fundamental relations, which lead to the occurrence of the molecular Kondo effect, in particular the nature of the involved single particle states and the local magnetic properties, are not completely clarified. In this respect angle-resolved photoelectron spectroscopy (ARPES) provides access to microscopic information, which is not or only very limited available by STM. Employing the angular information allows statements on the character and the symmetry of the involved localized states. In an ideal case molecular single particle orbitals can be reconstructed for organic adsorbate systems. Additional information is provided by investigating the dependence of the photoemission signal from the polarization direction and photon energy of the incoming light. Beyond this, the relevant model parameters can be derived from ARPES experiments, based on which a consistent picture of the microscopic relations in the Kondo model or Single Impurity Anderson Model (SIAM) can be obtained. Based on own previous work this project will systematically investigate the Kondo effect at molecule-metal interfaces by ARPES and in particular answer the following questions: (i) Which symmetry is associated with the many particle signals such as the Kondo resonance? What can we learn about the nature of these states from symmetries? The nature of the states involved in the occurrence of the Kondo effect is not yet clear and will be derived from the angular information in ARPES and from experiments with variable light polarization. (ii) Determination of the characteristic temperature- or energy scale from the temperature dependence of the Kondo resonance and core level spectra. The experimental determination of the temperature dependence of the photoemission intensities over a large temperature range provides access to the relevant characteristic energy scales. (iii) Can the relevant model parameters be systematically varied in practice? The description of molecule-substrate interface systems in the framework of the SIAM involves model parameters, which can be determined spectroscopically or by comparison to corresponding calculations. An external control of theses parameters allows manipulating the interface properties.